Is there a way to bake materials/textures, that use nodes, into materials/textures that can be used in the game engine?
Nothing really changes from a rectangular baking tutorial to anything else except for the UV mapping. Try using "Smart UV Project" to unwrap a complex object quickly, then go through the baking steps.


Add the image texture that you want to bake to in all of your materials (on the object that you are baking).
Setup the bake settings (depending on what you want to bake), then hit the bake button.
Save the baked image.